1. Field of the Invention
The present invention relates to a glow plug used for assisting start-up of a diesel engine and a method for manufacturing the glow plug.
2. Description of the Related Art
A glow plug used for assisting start-up of a diesel engine directly holds a heater having a heat generating resistor in an end part thereof which is in an end part of a tubular metal shell having a shaft hole, or the glow plug indirectly holds the heater via a holding member. In the shaft hole of the metal shell, a rod shaped intermediate shaft is inserted and arranged in an insulated state from the metal shell. One end part of the intermediate shaft is connected to a rear end part of the heater and the other end part protrudes from a rear end of the metal shell. Two electrodes taken out from the heater are electrically connected to the metal shell and the intermediate shaft, respectively.
A tubular insulator (an insulating member) is arranged in the rear end part of the metal shell, between the shaft hole and the intermediate shaft. The insulator has a collar part in a rear end side, and the collar part is held between a pin terminal or a circular nut attached to the other end part of the intermediate shaft and the rear end part of the metal shell to position the insulator. Thus, a part of the end side of the insulator from the collar part is arranged between the shaft hole and the intermediate shaft to ensure an insulating state between the metal shell and the intermediate shaft (for example, see Patent Literature 1). Further, in the rear end part of the metal shell, a seal member pressed and positioned by the insulator is arranged between the shaft hole and the intermediate shaft so that air-tightness in the shaft hole is ensured.
[Patent Literature 1] JP-A-2005-315474
3. Problems to be Solved by the Invention
However, the insulator used in a typical glow plug is formed in such a size as to provide a clearance between the insulator and the shaft hole and between the insulator and the intermediate shaft, respectively. In this manner, ease in an assembling operation is ensured during production. Therefore, in the rear end part of the metal shell, the intermediate shaft is of a form so as to be held by the seal member in a radial direction in the shaft hole. When a load is applied to the intermediate shaft due to vibration when driving a vehicle or due to attachment of a connector for supply of electric current, if the seal member is elastically deformed so that the intermediate shaft is deflected or bent in the shaft hole, there is a concern that stress may be applied to the heater connected to the one end part of the intermediate shaft.